Pressure relief devices for allowing pressurized dielectric fluid to escape from a transformer housing if the pressure in the housing increases, due either to an increase in ambient temperature or a fault in the transformer, have been known for many years. Known pressure relief devices of a particularly desirable type are designed so that once the release pressure is reached, a considerable amount of fluids, such as hot oil and gas, are released by the pressure release device in a very short time to rapidly reduce the pressure in the transformer housing, and prevent the housing from rupturing.
While high voltage transformers are often found in distribution facilities that are not manned, service must be performed from time to time and when operating personnel are working close to the transformers, the possibility for the release of fluid from a transformer during a fault is present. Typically when fluid is released it is extremely hot, possibly flaming, and poses a grave risk to anyone working close by. Pressure relief devices with integral shields for directing fluid released by the device to a ducting system are known.
Pressure relief devices, even devices of the same type are fitted to transformer housings in a variety of arrangements. More specifically, pressure relief devices are commonly provided with switches for sensing when the devices have been actuated and remotely signaling an operator, so that the cause for the excess pressure can be investigated. The position of such a switch on a pressure relief device may be different from one installation to another with respect to the possible orientation of a duct for receiving released fluid, and therefore a shield must have the capability of being oriented with respect to the pressure relief device and the switch in an orientation that permits coupling to the ducting, no matter how the pressure release device itself is oriented.
Pressure relief devices are typically fastened to transformer housings with a plurality of bolts or screws arranged in a circle. Where, as is common, six bolts are used, six different orientations of the switch, 60.degree. apart can be achieved. However, sometimes this is not precise enough to obtain the desired orientation of a shield with respect to the device, and a position between the positions available by selection of a mounting position on the circle must be utilized.
In addition to providing a device that accommodates the orientation of a switch wherever it may be found, it is desirable to provide a shield that allows the switch to be reset by an operator when a fault occurs. This requires manually operating the switch, and it is essential that the shield not interfere with such operation. Since the orientation of the switch with respect to the duct is arbitrary, it is not always possible to provide a fixed access opening in an integral shield for resetting the switch.
It is desirable to provide a shield that accommodates switch resetting in whatever orientation the switch might be found.
Many pressure relief devices are in service that would be prohibitively expensive to replace with integrally shielded devices. There is a need, therefore, for a versatile shield that can be retrofitted to pressure relief devices already installed on transformers.